One well known way to increase the performance of hard disk drives is to increase the areal data storage density of the magnetic hard disk. This can be accomplished by reducing the written data track width, such that more tracks per inch can be written on the disk. To read data from a disk with a reduced track width, it is also necessary to develop sufficiently narrow read head components, such that unwanted magnetic field interference from adjacent data tracks is substantially eliminated.
The standard prior art read head elements include a plurality of thin film layers that are deposited and fabricated to produce a GMR read head, as is known to those skilled in the art. Significantly, where the width of the thin film layers that comprise the GMR read head is reduced below certain values, the magnetic properties of the layers are substantially compromised. To overcome this problem, GMR read heads have been developed in which the thin film layers have an ample width, and bias layers and electrical leads are overlaid on top of outer “tab” regions of the thin film layers. This lead overlaid configuration has the effect of creating an active read head region having a width that is less than the entire width of the deposited layers, such that the magnetic properties of the thin film layers can be preserved. Thus, in the lead overlaid GMR read heads of the prior art, active magnetic layer portions exist between the electrical leads and passive magnetic layer portions exist beneath the electrical leads.
FIG. 1 is a side cross-sectional view of a prior art electrical lead overlaid read head portion of a magnetic head 100. As depicted therein, the prior art lead overlaid read head generally includes a substrate base 102 that constitutes the material from which the magnetic head is fabricated, such as aluminum titanium carbide. A first magnetic shield 104 is fabricated on the substrate, and an insulation layer 106, typically composed of aluminum oxide, is fabricated upon the magnetic shield 104. A seed layer 108 is deposited upon the insulation layer 106 and a series of thin film layers are sequentially deposited upon the seed layer 108 to form a GMR read head. In this structure, the layers generally include an antiferromagnetic layer 114, a pinned magnetic layer 118 that is deposited upon the anti ferromagnetic layer 114, a spacer layer 122 that is deposited upon the pinned magnetic layer 118, a free magnetic layer 126 that is deposited upon the spacer layer 122 and a cap layer 130 that is deposited upon the free magnetic layer 126. Typically, the antiferromagnetic layer 114 may be composed of PtMn, NiMn or IrMn, the pinned magnetic layer 118 may be composed of CoFe, the spacer layer 122 may be composed of Cu, the free magnetic layer 126 may be composed of CoFe and the cap layer 130 may be composed of Ta.
Following the deposition of the GMR read head layers 114–130, a patterned etching process is conducted such that only central regions 140 of the layers 114–130 remain. Thereafter, hard bias elements 148 are deposited on each side of the central regions 140. Following the deposition of the hard bias elements 148, electrical lead elements 154 are fabricated on top of the hard bias elements 148. As depicted in FIG. 2, inner ends 156 of the leads 154 are overlaid on top of tab regions 160 of the layers 114–130 of the central read head layer regions 140. A second insulation layer 164 is fabricated on top of the electrical leads 154 and cap layer 130, followed by the fabrication of a second magnetic shield (not shown) and further components that are well known to those skilled in the art for fabricating a complete magnetic head.
A significant feature of the prior art lead overlaid GMR read head depicted in FIG. 1 is that the portion of the central layer region 140 which substantially defines the track reading width W of the read head 100 is the central portion 144 of the read head layer regions 140 that is disposed between the inner ends 156 of the electrical leads 154. That is, because the electrical current flows through the read head layers between the electrical leads 154, the active portion 144 of the read head layers comprises the width w between the inner ends 156 of the electrical leads 154. The tab regions 160 of the read head layers disposed beneath the overlaid inner ends 156 of the electrical leads 154 are somewhat passive in that only a small amount of electrical current passes through them between the electrical leads 154.
A problem that has been recognized with regard to such prior art lead overlaid read heads is that the passive region of the magnetic layers of the read head, and particularly the free magnetic layer, is not entirely passive. That is, external magnetic fields, such as from adjacent data tracks, create magnetic field fluctuation and noise within the passive regions of the free magnetic layer beneath the electrical leads. Thus, noise and side reading effects continue to be a problem with lead overlaid GMR read heads.
Further, such prior art heads require hard bias material on either side of the sensor to exert magnetic force on the free layer to magnetically stabilize the free layer. The problem is that hard bias layers are very thick, and as track sizes shrink, sensors must get smaller. When the track width becomes very narrow, the hard bias layers make the free layer very insensitive and thus less effective. What is needed is a way to create a sensor with a narrow track width, yet with a free layer that is very sensitive.
To overcome the problems described above, designers have turned to providing in-stack bias layers in the tab regions. FIG. 2 depicts another prior art lead overlaid read head 200 having a structure similar to that of FIG. 1. As depicted in FIG. 2, the read head 200 includes a GMR read head thin film element 140, but does not include the hard bias elements, which have been replaced by an insulating material. Instead, this read head 200 includes bias layers 202 that are formed above the tab regions 160, such that an inner portion 204 of the layer 202 extends over the tab regions 160 of the layers that comprise the read head element 140. The bias layer 202 is deposited full film on top of an antiparallel (AP) coupling layer 206, the AP coupling layer providing antiparallel coupling between the bias layer 202 and the free layer 126. The AP coupling layer 206 is formed of Ru having a thickness of about 8 Å. The electrical leads 154 are thereafter fabricated on top of the bias layer 202. Then the portions of the leads 154 and bias layer 202 overlying the central portion 144 of the read head 200 are removed such as by etching (e.g., ion beam etching) or milling.
Because the inner portion 204 of the bias layer 202 are present only above the tab regions 160 of the AP coupling layer 206, which is deposited above the tab regions 160 of the free layer 126, the magnetic field within the inner portion 204 of the bias layers 202 will become magnetostatically coupled to the tab regions 160 of the free layer 126 through the AP coupling layer 206. This provides a pinning effect upon the magnetic fields within the tab regions 160 of the free layer 126, making the free layer 126 active only in the active area 144 and passive in the tab regions 160. The resulting structure is known as an AP-tab design.
A problem that has been recognized with regard to prior art lead overlaid read heads such as the head 200 shown in FIG. 2 is that during removal of the bias layer 202 from above the active region 144, the etching or milling can mill through the thin (8 Å) Ru AP coupling layer 206, resulting in damage to the underlying free layer 126. This damage in turn results in problems such as reading errors and instability. Also, it is desirable to avoid oxidation of the free layer 126. Removal of portions of the Ru coupling layer 206 exposes portions of the free layer 126, making it susceptible to corrosion.
What is therefore needed is a new structure that provides a thicker AP coupling layer that provides more protection to the underlying free layer during removal of the bias layer from the active portion of the read head.